1D Manholes: Difference between revisions
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=Manhole Losses=
When modelling conduit pipe flows, the head losses that the flow in pipe are subject to are made up of major losses (or friction losses) and minor losses (or local losses). Major losses are caused by forces between the flow and wetted perimeter of the conduit. Minor losses are caused by disruption to the flow due to bends, cross-sectional changes, fittings such as manholes and steps in the bed profile. Major losses are represented through the specification of a friction coefficient. The representation of minor losses, particularly for gravity networks, is at manholes and requires separate treatment. The default TUFLOW/Estry manhole loss approach uses the Engelund method explained in section 5.12.5.4 of the [https://www.tuflow.com/Download/TUFLOW/Releases/2018-03/TUFLOW%20Manual.2018-03.pdf| TUFLOW user manual] although it is also possible to use a more simplified fixed manhole headloss approach too using the global <font color="blue"><tt>Manhole Default Loss Approach</tt></font> command or specifying within the '1d_mH_*' layer in the Loss_Approach attribute. The Engelund approach provides an automatic method for determining the loss coefficients as presented below. Of note is that the coefficients are recalculated every timestep, and therefore vary depending on the flow distribution between inlet and outlet conduits and the depth of water within the manhole. The losses represented are as follows:<br>
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<li>'''K<sub>entry</sub>''' covers the expansion of flow within the manhole at the outlet of an inlet conduit. The coefficient is applied as the exit loss of the inlet conduit.
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<li>'''K<sub>drop</sub>''' is the loss coefficient due to a change in invert level and conduit height between inlet and outlet conduits.
<li>'''K<sub>Ɵ</sub>''' and '''K<sub>drop</sub>''' are added and applied as an energy loss for each outlet conduit.
<li>'''K<sub>exit</sub>''' covers the contraction from the manhole and re-expansion of flow within the entrance of an outlet conduit. It is applied as an entrance loss of the outlet.<br>
<li>'''K<sub>m</sub>''' is the user-defined manhole exit coefficient.
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The resulting headloss value is then applied, when sub-critical flow is experienced, to the standard head loss equation, i.e. dh = K*V<sup>2</sup>/2g. Where K is the loss coefficient, V is the conduit velocity and g the gravitational constant. The equations used for the Engelund loss approach are provided below:<br>
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[[File:Engelund Equations.PNG|500px]]
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<li>[[Manhole_Simple_Loss_Example#Example 1: Single Incoming/Outgoing Pipe with No Incoming Angle or Drop|Single Incoming/Outgoing Pipe with no angle and no drop]]
<li>[[Manhole_Simple_Loss_Example#Example 2: Single Incoming/Outgoing Conduit with Incoming Bend and Drop in Invert Levels|Single Incoming/Outgoing Pipe with incoming bend and drop in levels]]
<li>[[Manhole_Simple_Loss_Example#Example 3: Multiple Incoming Conduits with Incoming Bend and Drop in Invert Levels|Multiple Incoming Pipes with incoming bend and drop in levels]]<br>
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In the case of the fixed headloss approach, the 1d_mh_* K_Fixed attribute is applied to the standard head loss equation, i.e. dh = K*V<sup>2</sup>/2g on the outlet conduit(s).<br>
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